August 1949
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INDUSTRIAL AND ENGINEERING CHEMISTRY
the current proposed mechanism of light degradation, may be considered. One might be through eliminating the energy-absorbing polyene systems by use of “reactive molecules” as discussed previously. The other would be by utilizing antioxidants which would both reduce carbonyl formation and inhibit the free radical transmittance of ultraviolet light energy. To determine the effectiveness of antioxidant materials in promoting light stability in polyvinyl chloride plastics, compounds containing lead salicylate (an ultraviolet light absorber with some antioxidant properties) and di-tert-butyl-p-cresol (an active antioxidant) were prepared. One part of each of these materials was premixed with 65 parts of commercial polyvinyl chloride and 35 parts of di-2-ethyl hexyl phthalate, and mixed and sheeted in a 7minute milling cycle a t 135” C. As before, similar compounds were prepared with plasticizers that had been heated for 20 minutes at 163’ C., and all compounds were calendered into 12-mil sheets. Samples of the compound prepared from unaged plasticizer were heated t o 163 ” c. for 20 minutes to complete the duplication of previous test conditions. Table I11 summarizes the results of light exposure of these samples. The pronounced improvement in the light stability of the compound prepared with heat-aged di-2-ethyl hexyl phthalate is interesting. These results suggest that combinations of such antioxidant materials as those tested with other types of stabilizers would act t o enhance the over-all light resistance of the polyvinyl chloride plastic compound. SUGGESTED STABILIZING SYSTEM
On the basis of this investigation, the following stabilizing systems for polyvinyl chloride plastics may be suggested:
1. Agents capable of reacting with hydrogen chloride released during polymer breakdown and removing it as a n insoluble product. 2. Reactive dienophilic molecules capable of breaking up color-producing polyene systems resulting from the degradation reaction. 3. Selective ultraviolet light absorbers capable of reducing the total ultraviolet energy t h a t may be absorbed into the plastic oompound. 4. Antioxidants capable of inhibiting carbonyl formation within the polyenes and capable of inhibiting the facility of free radical transmittal of energy derived from unscreened incident ultraviolet light t o the unsaturated polyene systems within t h e polymer. ACKNOWLEDGMENT
The authors wish to express their appreciation t o B. A. Brice a n d M. L. Swain of the U. S. Department of Agriculture’s Eastern
1779
Regional Research Laboratory, and to the members of the National Lead Company’s Research Laboratory staff who assisted in this project. LITERATURE CITED
(1) Barnes, R. B., Gore, R. C., Liddel, U., and Williams, V. Z.,
“Infrared Spectroscopy,” New York, Reinhold Publishing Corp., 1944. (2) Boyer, R. F., J.Phys. & Colloid Chem., 51, 80 (1947). (3) Brode, W. R., “Chemical Spectroscopy,” 2nd ed., particularly Chap. VI-X, New York, John Wiley & Sons, 1943. (4) Carruthers, L. F., and Blair, C. M . , U. S. Patent 2,157,065 (May 2, 1939). (5) Daur, F., and Daniel, W., Ibid., 2,407,143 (Sept. 3, 1946). (6) Duggan, F. W., Ibid., 2,126,179 (Aug. 9, 1938). (7) Ellis, C., and Wells, A., revised by Heyroth, F. E., “Chemical Action of Ultraviolet Rays,” New York, Reinhold Publishing Corp., 1941. (8) Farmer, E. H., Bloomfield, G. F., Sudralingham, A , , and Sutton, D. A . 3Rubber Chem. Tech., 15,756 (1942). (9) Fuller, C. S., Chem. Rev., 26, 161 (1940). (10) Fuoss, R. M., Trans.Electrochem. Soc., 74, 110 (1938). (11) Furchgoth, R. F., Rosenkrantz, H., and Schorr, E., J. Bioi. Chem., 171, 523 (1947). (12) Hanson, A. W., and Goggin, W. C., U. S. Patent 2,273,262 (Feb. 17, 1942). (13) Holman. R. T.. Lundbern. W. 0.. and Burr. G. 0.. J . Am. Chem. Soc., 67, 1386 (1945). (14) Ibid., 67, 1390 (1945). (15) Land, E. H., and West, C. D., “Dichroism and Dichroic Polarizers” in Vol. VI of Alexander’s “Colloid Chemistry,” New York, Reinhold Publishing Corp., 1946. (16) Markley, K. S., “Fatty Acids,” particularly Chap XVI, New York, Interscience Publishers, 1947. (17) Marvel, C. S., and Homing, E. C., “Synthetic Polymers,” p. 754, Chap. 8, Vol. I, 2nd ed. of Gilman’s “Organic Chemistry, an Advanced Treatise,” New York, John Wiley & Sons, 1943. (18) Marvel, C. S., Jones, G. D., Mastin, T. W., and Schertz, G . L., J. Am. Chem. Soc., 64,2356 (1942). (19) Marvel, C. S., Sample, J. H., and Roy, M. F., Ibid., 61, 3241 (1939). (20) Matheson, L. A., and Boyer, R. F., manuscript in preparation. (21) Matheson, L. A,, and Boyer, R. F., U. S. Patent 2,287,159 (June 23, 1942). (22) Quattlebaum, W. M., and Noffsinger, C. A., Brit. Patent 557,477 (Nov. 19, 1943). (23) Quattlebaum, W. M., and Noffsinger, C. A., U. S. Patent 2,394,418 (Feb. 5, 1946). (24) Safford, M. M.,Ibid., 2,118,017 (May 17, 1938). (25) Ibid., 2,369,955 (Feb. 20, 1945). (26) Watson, J., Masland Duraleather Co., private communication. (27) Yngve, V., U. S. Patent 2,307,090 (Jan. 6, 1943). .
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RECEIVED April 28, 1948. Presented before the Division of Colloid Chema t t h e 113th Meeting of the AMERICAN CHEMICAL SOCIETY, Chicago, Ill.
istry
Isobaric Heat Capacity of 1-Butene and LPentene at Bubble Point W. G. SCHLINGER AND B. H. SAGE Culgornia Institute of Technology, Pasadena, Culv. T h e isobaric heat capacity at bubble point of 1-butene and 1-pentene was determined at temperatures from 90’ to 200’ F. These measurements were carried out in the two-phase region in a constant-volume adiabatic calorimeter. The isobaric heat capacity at bubble point was calculated from the directly measured isochoric values by use of supplementary volumetric data. The latter data were obtained experimentally for 1-butene and were estimated from the law of corresponding states for 1-pentene. The results are presented in graphical and tabular form.
T
HE information available concerning the heat capacity of
1-butene and 1-pentene in the liquid phase is limited t o measurements a t temperatures below 70” F. Aston et al. (1)presented heat capacities for liquid 1-butene a t temperatures from 20” t o 470’ Rankine. Huffman and co-workers (9) carried out measurements on the heat capacity of liquid 1-pentene in the temperature interval between 20’ and 530” Rankine. As a result of the absence of such data a t the high temperatures, a n investigation of the isobaric heat capacity of bubble-point liquid for 1-butene and I-pentene has been carried out.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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the dew-point gas.
Vol. 41, No. 8
The thelmal quantities in Equation 3,
g 92 - and 5 ,represent the net electrical energy required per unit
2910
y1
290C
O
B 2
ENERGY ADDITION
i 2790
x B 2780
-400
0
400 TlUE
800
1200
SECONDS
F i g u r e 1. V a r i a t i o n in Temperature of C a l o r i m e t e r with Time The measurements were made in the two-phase region utilizing I n order t h a t the directly measured information involving t,he energy required to heat the calorimeter bomb and content's through a predetermined temperature interval could be resolved into the isobaric heat capacity at bubble point, a t'hermodynamic analysis of the process was required. The calorimetric measurements were carried out with at least two different quantities of the pure hydrocarbon in the calorimeter. It, can be shown from a consideration of a material ba.lance and the h s t law of thermodynamics that for any twophase one-component system the follo.\vingequation applies:
a constant-volume calorimeter.
dT dT temperature change of the calorimeter bomb and its content?. These thermal quantities must be corrected for the thermal losses from the calorimeter and for the energy added in the course of t h e agitation of the contents of the calorimeter. Equation 3 indicates that the influence of the heat capacity of the dew-point gas on the heat capacity of the bubble-point liquid is relatively. small. This results from the fact' that the ratio of t,he specific volume of the bubble-point liquid t o that of the dew-point gas is small except in the vicinity of the critical state. For t,hisreason relatively large uncertainties in the isobaric heat capacity and in the isobaric volume-temperature derivative for dew-point gas d o not influence appreciably the resultant values of the isobaric hear capacity of bubble-point liquid. I n the case of 1-butene, the necessary volumetric data including the rates of change of bubble-point and dew-point, specific volumes with temperature and the rate of change of vapor pressure with temperature were obtained from published data ( 5 ) . It, is believed that t,hese values for l-butene were known with sufficient accuracy t o avoid introducing a n uncertainty greater than 0.27& in the final results. Since no volumetric data for 1-peritene were available for the temperature range covered by this investigation it was necessary to utilize information based on npentane ( 7 ) and the law of corresponding states ( 3 ) to establish the requisite volumetric behavior, This procedure should give results of sufficient accuracy for this use. The evaluation of the related terms of Equation 3 by such methods did not introduce added uncertainties of more than 0.3% in the final value oE the isobaric heat capacity of the bubble-point liquid. Values of the isobaric heat capacity a t dew point for 1-butene and 1pentene were t>akenas equal to the equivalcnt values for n-butane and n-pentane ( 4 ) . It is believed that the application of these data to the corresponding olefinic hydrocarbons did not introduce a significant uncertainty- in t.he results obtained from Lquation 3. APPARATUS AND PROCEDURE
+ (Ed - Eb)dmd
(1)
Considering the second law and applying Equation 1 to two different quantities of material in the bomb a t the same temperature there is obtained
+ ( T $ - P ) (Vd-
(
VI,) d m , - d m ,
)
Expressing (dmd, - dma,) and (mdl - mdz) in terms Vb, Vd, and ( m , - m z ) the following useful equation results, which applies to the processes in question:
Equation 3 required certain volumetric data concerning the material in question and includes the isobaric heat capacity of
The calorimetric equipment used in these studies was substnntially the same as t h a t employed in earlier investigations ( 2 , 6 ) . I n principle, t,he equipment consisted of a cylindrical steel container with hemispherical closures within which the hydrocarbon liquid was confined. Thermal equilibrium within the container was obtained by means of a small impeller rotating around an axi; coincident with t h a t of the calorimeter. Energy was added electrically t o the interior of the calorimeter by means of a short !ength of glass-insulat'ed constantan wire encased within a stainless steel tube approximately 0.05 inch in diameter. The ends of the steel tube were brought through the wall of the calorimeter with a sealed joint,. The quantity of electrical energy added t o the calorimeter wag determined by conventional volt box and standard resistance techniques. A potentiometer was employed to measure the electromotive force applied and the current) flowing through the calorimeter heater. It is believed that the rate of electrical energy addition t o the calorimeter was known with an uncertainty of less than 0.057,. Electrical energy was added t o the calorimeter for approximat,ely 500 seconds in t>hecase of each measurement,. The uncertaint'y in the determination of the total energy thus added to the equipment was less than 0.1%. T h e timing of the other events associated with the measurement of heat capacity was sufficiently accurate to int'roduce only a negligible uncertainty in the result. I n order t o decrease the thermal losses, the calorimeter was surrounded by an adiabatic jacket and the space between the jacket and the calorimeter was evacuated. Provision was made for the automatic maintenance of the average temperature of the interior surface of the jacket at substantially t h a t of the exterior. surface of the calorimeter. Measurements were carried out to cstablish the magnit,ude of the thermal losses as a function of the measured temperature difference between the calorimeter and the wall of the jacket. The energy transfers between the calorimeter jacket were in almost all cases less than 1% of the energy added t o the unit. The magnitude of this transfer was established with reasonable accuracy and it is believed that the uncertainties re-
August 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
1181
found in all cases t h a t agreement between the weight of material added and that withdrawn was within 0.1%. L
MATERIALS
0.42 d U
3
z0.40
I-1
z
dl
30.38
U
C
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II
The 1-butene used in this investigation was prepared by the dehydration of n-butyl alcohol with a n aluminum oxide catalyst at a temperature of 660" F. The crude material was fractionated twice a t atmospheric pressure in a column packed with glass rings a t a reflux ratio of 5 to 1. -4pproximately 15% of the overhead was discarded a t the beginning and end of each fractionation. The purified 1-butene exhibited a range in boiling point a t atmospheric pressure of less than 0.2"F. The 1-pentene was of research grade and was purchased from the Phillips Petroleum Company. The manufacturer's analyses indicated that i t contained less than 0.6 mole % of hydrocarbon other than 1-pentene, the probable impurity being isopentane. Because of the relatively small quantity of the sample available, the material was utilized without further purification except for two partial condensations a t liquid air temperature to remove any significant quantities of dissolved noncondensable gases. The 1-pentene after purification was handled in the same way as the 1-butene and was introduced into the calorimeter b y weighing bomb techniques (8).
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100
I20
140
TEMPERATURE
Figure 2.
I
Of
Calorimetric RIeasurements for 1-Butene
sulting from thermal losses were not greater than 0.15% of the corrected values of the energy added t o the calorimeter. The scheme of measurement involved the addition of a known weight of 1-butene or 1-pentene t o the calorimeter and determination of the net energy required to raise the temperature of the calorimeter and contents through a known temperature interval. For the purposes of these calculations it was assumed for the particular temperature interval in question that the following equation was applicable:
The left-hand side of Equation 4 was considered to apply a t the mean of the initial and &a1 temperatures. After completion of one su'ch series of measurements which extended over the entire temperature range investigated, additional material was added t o the calorimeter and the sequence of measurements repeated. For the most part the quantity of energy added electrically was adjusted t o yield a n over-all temperature rise of approximately 6" F. An effort was made t o carry out each set of determinations in accordance with a standardized procedure. The period allowed for the attainment of equilibrium after the addition of energy was used as the conditioning period for the next step. Figure 1 shows a typical set of time-temperature measurements for the calorimeter when i t contains 0.1987 pound of 1butene. I n this instance, thermal equilibrium was closely attained within 8 minutes after termination of the addition of energy. The variation in temperature in the calorimeter with time beyond this period was less than 0.002' F. per minute. Similar variations in temperature with time were obtained in the studies of 1-pentene. The samples were introduced into the calorimeter by use of high vacuum and weighing bomb techniques (8). It is believed that the weight of the sample introduced into the calorimeter was known within 0.02%. I n order t o check on this quantity and t o ascertain t h a t no loss occurred. the samdes were withdrawn after the completion of each set of measurements. It was
EXPERIMENTAL MEASUREMENTS
The experimental values obtained for the heat capacity of the bomb containing two different quantities of 1-butene are presented in Figure 2. The average deviation of the experimental points presented is 1.2% of the difference between the,two curves. As a part of Table I there are recorded experimental values of the heat capacity of the calorimeter and its contents a t several temperatures. This intermediate information is presented in order that the results may be re-evaluated if at a later date more accurate and complete volumetric measurements are available. The weights of the samples are included in Table I. Figure 3 presents information concerning the heat capacity of the calorimeter and its contents for three different quantities of 1-pentene. The average deviation of the experimental points shown from the curves drawn for this substance is also 1.2% of the difference between the curves. Table I contains values
TEMPERATURE
Figure 3.
OF
Calorimetric Measurements for 1-Pentene
INDUSTRIAL AND ENGINEERING CHEMISTRY
1782
Vol. 41, No. 8
a t several temperatures of the heat capacity of t h e Calorimeter with the three samples of I-pentene. RESULTS
Values of the isobaric heat capacity a t bubble point for 1-butene and 1-pentene are recorded in Table 11. A consideration of the accuracy of the measurement of the individual quantities involved indicates a n uncertainty of approximatcly 1% in the tabulated values. T o permit a direct comparison of the isobaric heat capacities recorded in Table I1 with the earlier measurements of Aston ( 1 ) and Huffman ( 9 ) , a graphical representation of the d a t a has been given in Figure 4. Reasonable agreement with the earlier measurements was obtained in the case of both compotmds. The curve shown for 1-butene represents the best estimate of the authors for the combined experimental results of Aston ( 1 ) and the new measurements presented in this discussion. The present data indicate a slightly smaller increase in the isobaric heat capacity a t bubble point with temperature for 1-pentene than would have been predicted from the earlier measurements of Huffman and co-workers (9) and the two sets of data have been indicated by separate curves. However, the discrepancy appears t o be less than the combined uncertainty of the two sets of data.
1 0
40
Figure 4.
I60
I20
80
TEMPERATURE
200
OF
Isobaric Heat Capacities at Bubble Points ACKNOWLEDGMENT
~~
Financial assistance from the California Research Corporation TABLEI. HEATCAPACITYOF CALORIMETER ASD CONTENTS and the interest of H. G. Vesper of that organization have made 1-Butene this work possible. The equipment employed mas developed as 0.052025 Lb.= 0.19872 Lb. a part of the activities of Project 37 of the American Petroleum Temp., ddT, Temp., g/dT, Institute. The cooperation of the American Petroleum InO F. B.t.u. j " F. F. B.t.u./O F. stitute in permitting the use of the calorimeter equipment in this 101.93 0.32119 116.10 0.40646 0.33067 121.62 0,40744 115.47 investigation is acknowledged 122.27 0.33159 127.23 n . 40962 128.96 135.65 142.22 148.73 155.25 161.73 181.29 187.65
0.33494 0.33645 0.33904 0.34098 0.34264 0.34801 0.35661 0.85520
132.60 137.80 143.20 148.81 154.24 159.56 164.71 175.59
0,41223 0.41825 0.42020 0.41764 0.42274 0.42609 0.42789 0.43529
1-Pentene 0.14215 Lb. 0.14200 Lb. Temp., q!dTi Temp., T F. B.t.u./' F. F. B.t.u./" F. 104.43 110.82 117.26 123.50 129.84 142.46 148.71 154.93 161.06 167.18 173.34 182.60 191.52 197.71 204.20 a T?Teight of material i n calorimeter.
0.03700 Lb. T e m p ., T, F, B . t . u . j 0 F. 91.40 0,30121 99 84 0.30402 107.83 0,30966 115.51 0.31142 B.31295 123.19 0.31517 130.92 0.31831 138.66 0.31942 147.27 0,32272 154.76 0.32536 162.02 0.32748 160.25 0,33337 191.32 0,83765 108.45
.... ,
.
I
.
.....
....
1-Butene
C, = isobaric heat capacity, B.t.u. per lb./" F. E = total internal energy, B.t.u. E = specific internal energy B.t.u. per lb. l,, = latent heat of pressure change, B.t.u. per lb./lb. pcr sq. in. m = weight of material in calorimeter, lb. P = ressure, lb./sq. in. abs. Q eat associated with process, B.t.u. infinitesima1,changc in state -p = heat associated T%*ith T = thermodynamic temperature, ' R. V = specific volume, cu. ft./lb. Subscripts A,B = state A and state B b = bubble point d = dew point = conditions with different quantities of sample in calorimeter Superscript " = two-phase state
=E
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LITERATURE CITED
TABLE11. ISOBARIC HEAT CAPACITIES OF ~-BGTENE AND ~-PENTENE AT BUBBLE POIKT Temp., F. 70a
NOMENCLATURE
1-Pentene
80Q 90a
100 110 120 130 140 150 160 170 180 190 200 210" 2205 LI Extrapolated. b Iaobrtric h e a t capacity at bubble point, B.t.u. per 1bJo F.
(1) Aston, J. G., Fink, H. L., Bestful, -4., Pace, E. L., and Szasa, G . J., J. Am. Chem. SOC., 68, 52 (1946). (2) Budenholzer, R. A., Sage, B. H., and Lacey, W. N., IND. ENG. CHEM.,35, 1214 (1943),
(3) Gibbs, J. W., Trans. Conn. Bcad.,3,108 (1876). (4) Kennedy, E. R., Sage, B. E., and Laces, W. N., IKD. ENCI, CHEM.,28, 718 (1936). ( 5 ) Olds, R. H., Sage, B. €I., and Lacey, W. X., Ibicl.. 38, 301 (1946). (6) Sage, B. II., Evans, H , D., and Lacey, W. X., lbicl , 31, 763 (1939). (7) Sage, B. H., and Lacey, W.N., Ibid., 3 4 , 7 3 0 (1942). (8) Sage, B . H., and Lacey, W. N., Trans. Am. Inst. M
